AD8328ACPZ datasheet(13/20 Pages) AD

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AD8328

Rev. A | Page 13 of 20

DIFFERENTIAL SIGNAL SOURCE

Typical applications for the AD8328 use a differential input

signal from a modulator or a DAC. See Table 7 for common

values of R4, or calculate other input configurations using

Equation 2. This circuit configuration will give optimal

distortion results due to the symmetric input signals. Note

that this configuration was used to characterize the AD8328.

−

kΩ

1.6

kΩ

1.6

(2)

VIN+

VIN–

AD8328

ZIN

Figure 21. Differential Circuit

DIFFERENTIAL SIGNAL FROM SINGLE-ENDED

SOURCE

The default configuration of the evaluation board implements

a differential signal drive from a single-ended signal source.

This configuration uses a 1:1 balun transformer to approximate

a differential signal. Because of the nonideal nature of real

transformers, the differential signal is not purely equal and

opposite in amplitude. Although this circuit slightly sacrifices

even-order harmonic distortion due to asymmetry, it does

provide a convenient way to evaluate the AD8328 with a single-

ended source.

The AD8328 evaluation board is populated with a TOKO

617DB-A0070 1:1 for this purpose (T1). Table 7 provides

typical R4 values for common input configurations. Other input

impedances can be calculated using Equation 3. See Figure 26

for a schematic of the evaluation board. To use the transformer

for converting a single-ended source into a differential signal,

the input signal must be applied to VIN+.

−

kΩ

1.6

kΩ

1.6

(3)

AD8328

VIN+

ZIN

Figure 22. Single-to-Differential Circuit

SINGLE-ENDED SOURCE

Although the AD8328 was designed to have optimal DOCSIS

performance when used with a differential input signal, the

AD8328 can also be used as a single-ended receiver, or an IF

digitally controlled amplifier. However, as with the single-

ended-to-differential configuration previously noted, even-

order harmonic distortion is slightly degraded.

When operating the AD8328 in a single-ended input mode,

VIN+ and VIN– should be terminated as shown in Figure 23.

On the AD8328 evaluation boards, this termination method

requires the removal of R2 and R3 to be shorted with R4 open,

as well as the addition of 82.5 Ω at R1 and 39.2 Ω at R17 for

75 Ω termination. Table 7 shows the correct values for R11

and R12 for some common input configurations. Other input

impedance configurations can be accommodated using

Equation 4 and Equation 5.

−

800

(4)

(5)

R17

AD8328

VIN+

ZIN

Figure 23. Single-Ended Circuit

Table 7. Common Matching Resistors

Differential Input Termination

ZIN (Ω)

R2/R3

R4 (Ω)

R1/R17

Open

51.1

Open/Open

Open

78.7

Open/Open

100

Open

107.0

Open/Open

150

Open

165.0

Open/Open

Single-Ended Input Termination

ZIN (Ω)

R2 (Ω)/R3 (Ω)

R4 (Ω)

R1 (Ω)/R17 (Ω)

0/0

Open

53.6/25.5

0/0

Open

82.5/39.2

OVERSHOOT ON PC PRINTER PORTS

The data lines on some PC parallel printer ports have excessive

overshoot that can cause communication problems when

presented to the CLK pin of the AD8328. The evaluation

board was designed to accommodate a series resistor and

shunt capacitor (R2 and C5 in Figure 26) to filter the CLK

signal if required.

INSTALLING VISUAL BASIC CONTROL SOFTWARE

Install the CabDrive_28 software by running the setup.exe file

on Disk One of the AD8328 evaluation software. Follow the on-

screen directions and insert Disk Two when prompted. Choose

the installation directory and then select the icon in the upper

left to complete the installation.

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